Thursday, January 27, 2011

Over the years Paul Truong has been using vetiver for various applications, one of them being for flood control at Laidley, Queensland.

The above Google Earth image shows quite clearly (left of yellow pin) vetiver hedgerows planted circa 2004. The location (27°38'19.20"S 152°23'54.21") was a choke point in the natural drainage system that was eroding badly from water inflow (red arrows) from higher up. The purpose of the hedgerows was to reduce the velocity of flood water and to stop erosion of the this area and reduction of bank erosion further down stream. Downstream (blue arrow) the flood water was more confined. Further down you can see from Google Earth imagery (not included here) that just before Ambrose Street in Laidley that the drainage bank has been protected with vetiver.

Paul Truong recently visited this site after the recent flood, he writes ..... "Incredible, the water must have been at least > 3m above vetiver and fast enough to lift these concrete setting fence post and shifted this full (not empty) container from 10 km up stream to next to the vetiver planting. The planting partially save the town from deeper flood as it held back and slowed down the water. I talked to the lady living in the house next to the planting (see the Google Pix blue roof) and she blamed vetiver for backing up so much water that it flooded her house. But she agreed with me that if all that water had gone unimpeded down stream it would have made the flooding worse in the town."

Note the bottom image - 3 meters of water had crossed these hedgerows a few weeks ago - one would not know it! - and there is no erosion.

A few lessons to be learned?

We will be receiving more from Paul of other flood sites in the near future.